The invention relates to a magnetic domain arrangement for single wall magnetic domains which are created in said arrangement by means of a magnetic field and which only exist for magnetic field values comprised between two different values thereof, said arrangement including a plurality of co-planar paths and means which are able to propagate said domains along said paths, at least three of which having a path part in proximity of each other whereby a magnetic domain moving on said path part of a first one of said paths may be deviated into a second one of said paths due to the mutual repelling force of said magnetic domain and a second magnetic domain on said third path part.
Such an arrangement is known from the U.S. Pat. No. 3,770,978. In this patent an AND gate is described using the well known magnetic domain technology. A general description concerning the techniques used and the magnetic domains themselves and their propagation is described in the article "Magnetic Bubbles--An Emerging New Memory Technology" by A. H. Bobeck, P. I. Bonyhard and J. E. Geusic published on pages 1176 to 1194 of the Proceedings of the IEEE Vol. 63, No. 8, August 1975. In the method of propagation described therein and which is used in the present invention the magnetic domains or bubbles which can be considered as small magnetic dipoles move in a magnetic layer such as orthoferrite under the influence of the attracting and repulsive forces of successive magnetic poles created into an iterative permalloy pattern deposited on the magnetic layer and follow a path defined by the successive magentic poles. The magnetic poles are induced by an inplane rotating magnetic field parallel to the layer surface and the iterative permalloy pattern may for instance be constituted by a number of T- and bar-shaped elements. A bias field perpendicular to the surface of the layer is used to determine a given bubble diameter. There are two critical bias field values for a given magnetic layer material, i.e., the collapse and the strip-out bias field strength values. For a bias field strength value smaller than the strip-out value, strip domains develop whose magnetization is reversed to that in the remainder of the magnetic layer. When this field strength increases, the bubble diameter decreases until it collapses at the collapse field strength value. In the gate represented in FIG. 7c of the above mentioned U.S. Patent a bubble (21) (called information bubble hereinafter) in an input channel (x.sub.1 for instance), is deviated into an output channel (y.sub.1) due to the repelling force of a control bubble (44) in a control channel (Z), the control bubble occupying a very stable position in the neighborhood of the output channel to deviate the information bubble from the input channel into the output channel. In this patent no mention is made of the relative distances of the bubble paths in proximity of each other, i.e., the distance between the control bubble and the information bubble (21) prior to its deflection into the output channel and the transmission distance separating the input channel and the output channel to be covered by the information bubble when being deflected from the input path into the output path. These relative distances are however, very important since they influence the bias margin which is the ratio of the difference of the collapse and strip-out bias field strength values and the mean value thereof.
Indeed, the length of this transmission distance influences the collapse field strength in an inversely proportional way. When this length increases or decreases the collapse field strength decreases or increases respectively. This is easily conceivable when it is realized that a bubble has a more stable position when located under a permalloy element of a pattern of a path than when situated in an uncovered area of the magnetic layer. However, the above transmission distance cannot be decreased below predetermined limits, i.e., not much below a nominal bubble diameter. When this would happen a bubble moving in the input channel in the neighborhood of the output channel and without the presence of a control bubble for instance may merge into one large bubble connecting both channels and may further be split, one split half continuing its way on the input channel whilst the other half further propagates on the output channel. This, of course, entails an erroneous operation of the gate. On the other hand, the repelling force of the control and information bubbles decreases with the distance increase between these two bubbles at the deflection point of the gate. When this distance increases beyond a predetermined value the repelling force may be too low to deflect the information bubble into the output channel which again entails an erroneous operation of the gate, whereas when this distance is too small the information bubble may collapse when the control bubble is in a very stable position near the deflection point.
From the above it follows that in order to reach operating bias margins as large as possible and at the same time to assure good operating conditions of the gate certain design rules have to be taken into account.
It is an object of the invention to realize such a magnetic domain gate arrangement.